[Steeveedee]

Those are meant for single flare lines, just so you know. But they will conform to the double flare fitting, so it's all good. We used those to seal up single flare fittings on spacecraft fuel systems, which have to not leak for the lifetime of the thing, which might be 30 years or so, like the Hubble (which I did not work on); just pointing out an old system that is still working. If you break the fuel lines open, you should either use new conical washers or anneal the ones you removed in the oven, provided they are not dented. If dented, just toss them. Do know, however, that many millions of vehicles rolled off the assembly without washers in the fittings.